Blood Stain Pattern Analysis Lecture

Introduction

• Presenter: Matthew Steiner, certified senior crime scene analyst.
• Focus: Techniques used to analyze various bloodstain patterns in forensics.
• Importance: Safety at crime scenes, avoiding contamination.

Safety Precautions

• Personal Protection Equipment (PPE):
  • Multiple layers of gloves.
  • Eye protection (for splash hazards).
  • Tyvek suit (covers body and feet).
  • Mask (though not worn on camera).

Types of Blood

• Defibrinated Sheep's Blood:
  • Fibrin removed to prevent clotting.
  • Used for demonstration purposes.

Analyzing Blood Stains

• General Approach:
  • Analysts correlate bloodstain appearance with the mechanism of creation.
  • Not a 'crystal ball' but a method to deduce possible actions.

Categories of Bloodstains

1. Passive Patterns

   • Created by gravity or contact.
   • Surface Texture Impacts:
     • Smooth surfaces: even, round circles.
     • Textured surfaces (tile/wood): scalloping or spiny edges, satellite stains.
   • Examples:
     • Suspect blood trails (e.g., from a cut).

2. Contact Transfer Stains

   • Occurs when a bloody surface contacts another surface.
   • Examples:
     • Shoe prints, handprints, weapon imprints.
     • Moving a bloody object: creates 'Feathering' patterns.
     • Drag marks of a bleeding victim.

3. Flow Patterns

   • Movement of blood volume due to gravity.
   • Examples:
     • Blood flowing down an arm.

4. Saturation and Pooling Patterns

   • Accumulation of blood on surfaces.
   • Examples:
     • Pooling on non-porous surfaces.
     • Saturation showing slow drying/clotting.
     • Serum separation observed.

5. Spatter Patterns

   • Result of external force on open blood sources.
   • Impact Spatter Analysis:
     • Directionality determined by angle of blood hits.
     • Common in bludgeoning, shootings (forward and back spatter).

Advanced Analysis

1. Area of Convergence

   • Determining the 2D space from which blood originated.
   • Draw lines through stain axes to find convergence.

2. Angle of Impact Determination

   • Measure length and width of stains.
   • Use trigonometry (arc sine) to find impact angle.

3. Area of Origin Determination

   • 3D space calculation using trigonometry.
   • Helps to visualize the blood source position above the surface.

Interpreting Relationships

• **Example Situations: **
  • Passive stain under clothing: indicates sequence of events.
  • Feathering in blood trails indicating direction of movement.
  • Distinguishing Swipe vs. Wipe: Movement directionality.
  • Cast-off patterns: Objects flinging blood (hand, pipe, bat, etc.).
  • Void patterns: Something blocking or being removed from blood spray.

Summary

• Bloodstain pattern analysis is complex and requires significant training and experience.
• Not absolute; multiple interpretations are possible.
• Aim: Educate on methods and considerations in bloodstain analysis.